a) Field of the Invention
The invention is directed to a process for measuring taper threads on a coordinate measurement device which is outfitted with a table adjustable in the X, Y and Z coordinates for receiving a specimen provided with the taper thread and which further comprises a feeler probe which is held at a spring clip such that its position is adjustable in the Z direction and which is connected by this spring clip with a measurement sleeve which is adjustable in the X direction and at which is arranged a sensing element which can be deflected in the X coordinate, wherein a calibration of the feeler probe is initially carried out with reference to a setting gage, wherein, after calibration, the sensing element is brought into contact with different thread flanks one after the other for the purpose of measuring the taper thread, the measurement values determined in this way are stored in an evaluating unit and the characteristic values and fundamental quantities of the taper thread are calculated on the basis of the stored measurement values.
b) Description of the Related Art
The invention is especially suited for determining the flank diameter of taper threads. The flank diameter is determined in a testing plane which is at a determined distance from an end face of the specimen; DIN 158 (metric tapered external thread) and DIN 2999 (Withworth pipe thread), among others, are taken into account.
DIN 158 and DIN 2999 set forth the characteristic values and fundamental quantities for tapered external thread and, at the same time, provide directions for a simple and direct functional testing of this thread. Suggestions are made for the construction and handling of gages by which the fundamental quantities of a taper thread can be tested. For this purpose, there are provided taper thread ring gages or thread plug gages which only enable testing of the thread, but not measurement of the thread.
For example, the flank diameter of a taper thread can be determined in that a plug gage with a cylindrical thread is screwed into a tapered internal thread; the value of the flank diameter must then be derived from the screw-in depth in a corresponding measurement plane. The flank diameter cannot be exactly determined in this way.
Further, it is known to use the three-wire method, as it is called, to measure tapered external threads. This method is described, for example, in Langsdorf, "Messen von Gewinde [Measurement of Thread]", Springer-Verlag Berlin, Heidelberg, New York, 1974, pages 69 to 74, and in Zill, "Messen and Lehren im Maschinen-und Feingeratebau [Measurement and Gaging in Mechanical and Precision Instrument Engineering]", Deupner Verlagsgesellschaft, Leipzig 1956, pages 183 and 184.
This measurement process has the disadvantage of being quite time-consuming because, in addition to the thread measuring wire set, it requires thread measurement balls of identical diameter and associated centering sleeves which must be fitted to the complementing spindle.
A process and an arrangement for measuring taper thread on a coordinate measurement device is known from DE-PS 44 10 195.3. In this case, after a measurement feeler has been calibrated, the specimen is clamped on the coordinate table by means of a calibrating ring. The table is tiltable and is initially adjusted in such a way that a first flank diameter line of the taper thread is oriented parallel to the Z coordinate. In this position, the thread is sensed repeatedly in different Z coordinates. The inclination of the table is subsequently changed in such a way that a second flank diameter line located diametrically opposite to the first flank diameter line is oriented parallel to the Z coordinate. In this case, also, the thread turns are sensed repeatedly in different Z positions. Measurement values are determined for every instance of sensing and are stored in an evaluating device. The characteristic values and fundamental quantities of the taper thread are determined from the stored measurement values based on known geometric relationships. A disadvantage in this process consists in that the table must be tiltable, which requires an additional articulation axis for its bearing support and, to this extent, involves the risk of inaccuracy due to manufacturing tolerances.
A process and a device for the measurement of tapered external thread are known from the German Patent 195 22 276 C1. In this case, a single-coordinate measurement device is provided for carrying out the process, wherein the specimen with the thread to be measured is received on a slide which is adjustable in three coordinate axes and is sensed by a feeler probe arranged at the measurement sleeve of the single-coordinate measurement device. It is disadvantageous that the process and device described above are not suitable for the measurement of internal thread.